The present invention relates to composite elements having the following layer structure:
(i) 2-20 mm, preferably 5-20 mm, particularly preferably 5-10 mm, of metal,
(ii) 10-100 mm of compact polyisocyanate polyaddition products obtainable by reacting (a) isocyanates with (k) polyether polyalcohols, if desired in the presence of (c) catalysts and/or (d) auxiliaries and/or additives,
(iii) 2-20 mm, preferably 5-20 mm, particularly preferably 5-10 mm, of metal.
The invention further relates to a process for producing these composite elements and to their use.
The construction of ships, for example ships"" hulls and hold covers, bridges or high-rise buildings require the use of structural components which can withstand considerable external forces. Owing to these requirements, such structural components usually comprise metal plates or metal supports which are strengthened by means of an appropriate geometry or suitable struts. Thus, hulls of tankers usually consist, because of increased safety standards, of an inner and an outer hull, with each hull being made up of 15 mm thick steel plates which are connected to one another by steel struts about 2 m long. Since these steel plates are subjected to considerable forces, both the inner and outer steel shells are reinforced by welded-on reinforcing elements. Disadvantages of these classical structural components are both the considerable amounts of steel which are required and the time-consuming and labor-intensive method of manufacture. In addition, such structural components have a considerable weight resulting in a lower tonnage of the ship and increased fuel consumption. Furthermore, such classical structural elements based on steel require a great deal of maintenance since both the outer surface and the surfaces of the steel parts between the outer and inner shells regularly have to be protected against corrosion.
It is an object of the present invention to develop structural components which withstand high external forces and can he used, for example, in shipbuilding, bridge construction or construction of high-rise buildings. The structural components to be developed, also referred to as composite elements, should be able to serve as replacements for known steel structures and, in particular, have advantages in respect of weight, production process and maintenance requirements. In particular, the composite elements should be able to be produced simply and quickly in large sizes and also be able to be used in shipbuilding due to improved resistance to hydrolysis.
We have found that this object is achieved by the composite elements described at the outset.
The composite elements of the present invention are produced using polyether polyalcohols for the reaction with the isocyanates. The use of polyether polyalcohols offers substantial advantages due to improved resistance of the polyisocyanate polyaddition products to hydrolytic cleavage and because of the lower viscosity, in each case compared to polyester polyalcohols. The improved hydrolysis stability is particularly advantageous for use in shipbuilding. The lower viscosity of the polyether polyalcohols and the reaction mixture comprising the polyether polyalcohols for preparing (ii) makes possible more rapid and simpler filling of the space between (i) and (iii) with the reaction mixture for producing the composite elements. Owing to the considerable dimensions of, in particular, structural components in shipbuilding, low-viscosity liquids offer a considerable advantage.
The composite elements of the present invention can be produced by preparing, between (i) and (iii) compact polyisocyanate polyaddition products which adhere to (i) and(iii) by reacting (a) isocyanates with (b) polyether polyalcohols, if desired in the presence of (c) catalysts and/or (d) auxiliaries and/or additives.
The surfaces of (i) and/or (iii) to which (ii) adheres after production of the composite elements are preferably sandblasted. This sandblasting can be carried out by conventional methods. For example, the surfaces can be blasted with customary sand under high pressure and thus, for example, cleaned and roughened. Suitable equipment for such treatment is commercially available.
This treatment of th surfaces of (i) and (iii) which ar in contact with (ii) after the reaction of (a) with (b), if desired in th presence of (c) and/or (d) leads to considerably improved adhesion of (ii) to (i) and (iii). Sandblasting is preferably carried out immediately before introduction of the components for preparing (ii) into the space between (i) and (iii).
After the preferred treatment of the surfaces of (i) and (iii), these layers are preferably fixed in a suitable arrangement, for example parallel to one another. The spacing is usually selected such that the space between (i) and (iii) has a thickness of from 10 to 100 mm. (i) and (iii) can, for example, be fixed in place by means of spacers. The edges of the intermediate space are preferably sealed such that the space between (i) and (iii) can be filled with (a) and (b) and, if desired, (c) and/or (d) but these components are prevented from flowing out. Sealing can be carried out using customary plastic films or metal foils and/or metal plates which can also serve as spacers.
The layers (i) and (iii) are preferably customary metal plates, for example steel plates, having the thicknesses according to the present invention.
The space between (i) and (iii) can be filled either with (i) and (iii) aligned vertically or with (i) and (iii) aligned horizontally.
The filling of the space between (i) and (iii) with (a), (b) and, if desired, (c) and/or (d) can be carried out using feeding equipment, preferably continuously, for example by means of high- and low-pressure machines, preferably high-pressure machines.
The feed rate can be varied depending on the volume to be filled. To ensure homogeneous curing of (ii), the feed rate and the feeding equipment are selected such that the space to be filled can be filled with the components for preparing (ii) within 5-20 minutes.
As layers (i) and (iii), usually plates, use can be made of customary metals, for example iron, conventional steel, all types of alloy steel, aluminum and/or copper.
Both (i) and (ii) can be used in coated form, for example primed, painted and/or coated with customary plastics, for producing the composite elements of the present invention. Preferably, (i) and (iii) are us d in uncoated form and are particularly preferably cleaned, for example by customary sandblasting, before use.
The preparation of the compact polyisocyanate polyaddition products (ii), usually polyurethane and, if desired, polyisocyanurate products, in particular polyurethane elastomers, by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates, if desired in the presence of (c) catalysts and/or (d) auxiliaries and/or additives has been described many times. For the purposes of the present invention, compact polyisocyanate polyaddition products are ones which have no cellular structure as is customary, for example, for polyurethane foams. To achieve this compact structure, the addition of blowing agents to the starting components for preparing (ii) is avoided. To substantially avoid a foaming process, both the starting components (b) and, if used, (c) and (d) and also the surfaces of (i) and (iii) with which the reaction components come into contact should preferably be dry.
The water content of the reaction mixture comprising (a), (b) and, if used, (c) and/or (d) is preferably from 0 to 0.03% by weight, based on the weight of the reaction mixture. The water content of, in particular, the component (b) can be reduced to the appropriate level by, for example, distillation. It is also possible to add compounds which bind water and thus prevent a blowing reaction to the reaction mixture. Such compounds, for example molecular sieves, are generally known. For example, it is possible to use silicates and oxazolidines in a suitable, preferably finely divided, form. These compounds are preferably added to the reaction mixture, preferably the component (b), in amounts of from 0.05 to 5% by weight, based on the weight of the reaction mixture.